This invention relates to a crank mechanism which is especially useful in physical rehabilitation programs and in bicycle pedaling mechanisms. The mechanism of the invention provides an easily adjustable circular and/or elliptical path of travel for the handles or pedals associated with such mechanisms.
Although the invention is adaptable to a wide variety of crank-type applications, it is particularly useful in physical therapy applications, in which it is frequently necessary to have a patient's limbs repeatedly trace circular or elliptical patterns or to simulate motions and exercises such as rowing.
The range of physical therapies which can be achieved with the invention is substantial. Some patients require treatment involving a degree of positive resistance on a crank mechanism; for these patients, proper therapy includes the patient forcing the crank to move. For other patients it is a great achievement to merely have their limbs pulled through a certain movement pattern; the crank has to provide the motive force for these patients' therapy. Depending upon the particular needs of the patient, appropriate therapy may include treatment of both arms or both legs, either simultaneously or individually, as well as treatment of only one arm or one leg.
Furthermore, patients' needs vary widely with respect to the height and orientation at which the crank-related movement is most beneficial. For optimum flexibility and usefulness, therefore, a crank mechanism for physical therapy must be readily portable and mountable or otherwise adjustable into a range of positions and locations.
Moreover, the crank mechanism of the present invention adds a further dimension to physical therapy by providing the ability to adjust the pattern of movement incrementally, such as changing from a relatively flat elliptical pattern gradually to a circular pattern or vice versa, as the patient improves. Except for the mechanism of the invention, the inventors are not aware of any equipment available for use in physical therapy which can achieve the adjustable elliptical patterns of the present invention.
Obviously, a crank mechanism which can meet this broad range of needs is extremely valuable in the field of physical therapy, in that it will reduce the cost of buying, storing, and maintaining many pieces of equipment to achieve the same ends. Ideally, and perhaps most importantly, such a device allows a therapist to customize the treatment to the particular patients' needs.
As indicated above, the invention is also directly applicable to bicycle pedalling mechanisms. For many years, attempts have been made to modify the standard bicycle pedalling mechanism to improve its energy efficiency and its ease of use, and to reduce the perceived boredom of repeatedly moving one's legs and feet through a circular pedal path. Certain devices, such as U.S. Pat. Nos. 4,706,516 to La Xi and U.S. Pat. No. 4,159,652 to Trammell, Jr., have retained the circular pedal path and focused solely on improving the energy efficiency. Other devices have used relatively fixed linkage and/or gear combinations to achieve a pedal path which is oval (U.S. Pat. No. 4,173,154 to Sawmiller), elliptical (U.S. Pat. No. 4,193,324 to Marc), spiral, or cardioidal (U.S. Pat. No. 3,865,366 to Stantial).
Although certain of the aforementioned prior art devices have achieved non-circular pedal motion, the particular motion of each is relatively fixed by the structure and dimensions of the particular components used therein. These prior art devices do not exhibit the ease and degree of adjustability achieved by the present invention, and certainly do not provide the flexibility of application desirable in an exercise rehabilitation mechanism appropriate for physical therapy.